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The Road Cyclist's Guide to Training by Power
by Charles Howe
with contributions from Andrew Coggan, Ph.D.
Third Edition, October 2003


Perhaps unique among all endurance athletes, cyclists have the capability of accurately measuring their external work rate, or mechanical power output, while “in the field,” i.e., on the road or track, through commercially available power-measuring systems such as the Polar S-710, Power-Tap, and SRM (Schoberer Rad Messtechnik) Training System.  These hold great potential as training aids, since power is an objective measure of the stress load, or intensity, being imposed, and as such directly determines physiological and perceptual responses to exercise.  They are particularly appropriate for road cycling, where the resistive forces to forward motion vary greatly from one moment to the next in relation to terrain, wind velocity and direction, changes in speed, and road conditions.  Indeed, many react with disbelief at how “jumpy” the current power display is when using any of these devices for the first time, and question the readout’s reliability.  This is a result of having become accustomed to the heart rate monitor (HRM) as a gauge of intensity, and being fooled by its delayed response to changes in intensity into thinking that the energy requirements of cycling are relatively steady, however, the accuracy of the power meter (and hence, the variable, or “stochastic” nature of on-road power expenditure) is verified by checking it against any constant-load indoor trainer. 


Cyclists have at times taken their cue from distance runners in adopting pacing guidelines to gauge intensity for flat-terrain workouts.  The concept of goal pace and date pace was borrowed from perhaps its most widely known advocate, University of Oregon coach Bill Dellinger.  This approach may have some reliability at a given velodrome, so long as temperatures do not vary significantly and the air is calm, but is unlikely to be useful on the road, even under ideal conditions, with the possible exception of a standard (and sufficiently steep) uphill course.


The ‘paradigm’ for measuring exercise intensity was changed in the mid-1980s, when accurate, reliable, and affordable HRMs the size of a wristwatch began to reach the consumer market. As becomes apparent when correlated with power, however, heart rate is limited not only by its slow response to changes in power, but also since it can vary widely for a given wattage (much moreso during outdoor cycling, as compared to indoors on a constant-load ergometer)due to physiological and environmental factors.  Indeed, had power meters preceded HRMs, the latter might have never been marketed and sold as a separate device.  


Intensity may also be gauged by “feel,” or perceived exertion (PE), either on a 10-point scale, or the original 6-20.  PE is subjective in nature, with its precision limited accordingly, and yet, perceptual responses to exercise are an important source of feedback during training, since they actually integrate more physiological information than HR.  Still, only occasional reference will be made here other than to power as a measure of intensity.


Finally, power-based training has long been possible with a calibrated bicycle ergometer, but the first power-measuring device for use “on the road” did not appear until 1988, when the SRM system was introduced.  It was followed by the Power Pacer (Balboa Instruments) and Look Max One hubs in the early ’90s, neither of which was a commercial success.  SRM received a significant boost when it was embraced by several national cycling federations, as well as numerous professional  and elite riders, including Greg LeMond, but it took the Power Tap (1998, Tune Corp., purchased by Graber Products in late 2000) and Polar S-710 (2001) to bring accurate and reliable power measurement within reach of most any rider.  (Ciclosport models are not mentioned here, since they make only a crude estimate of power, based on weight, speed, and gradient.)

benefits of power-based training

1. It eliminates guesswork from gauging exercise intensity.  Even those with exceptional “feel” are unlikely to judge their wattage any better than to within perhaps 10%, whereas a power meter is accurate to ±2% or less.

2. It allows fitness to be precisely and accurately quantified and tracked, both daily and over time.  Workouts become carefully controlled, and along with a periodized program, training is less haphazard, making peak performances easier to predict.  Carefully planned training may also help prevent overtraining and injury.

3. Power meters have other uses, such as pacing during interval training, time trials, and even breakaways in mass start races; aerodynamic testing; and possibly as an aid to dieting and weight control.  Previously, wind tunnel testing was necessary to assess air drag, but under carefully controlled conditions, it may be possible to do this in the field.

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